The present invention relates to an on-screen display (OSD), and more particularly, to an apparatus for performing various on-screen display functions for displaying a character on a screen in various forms and a method for performing each function.
An OSD apparatus generates and displays a character in similar manner to a typical liquid crystal display (LCD) controller. However, unlike an LCD controller, the OSD apparatus displays the character together with a moving picture signal.
The OSD apparatus separates and detects horizontal and vertical synchronous signals from a composite synchronous picture signal and uses the detected horizontal and vertical signals as picture synchronous signals. An Automatic Frequency Controller (AFC) is then used to display the character synchronized with the picture signal without scattering or distortion. The AFC is part of the Phase Locked Loop (PLL) and can be any one of various types. Typically, a Frequency Synthesized PLL is used for on screen displays. The PLL is used for compensating for the phase and frequency difference of the external composite video signal. However, in the prior art, the state of synchronous signals included in the external composite video signal is erratic when a pseudo composite video signal including, for example, a guard signal, is input to the frequency synthesized PLL. The PLL cannot compensate well for erratic synchronous signals present in the composite video signal. Also, in a conventional OSD apparatus characters are displayed on a background screen or with a video signal.
Thus, there is a need for an OSD apparatus which includes new and convenient functions, consumes less power, and is small and lightweight.